Transmission of COVID-19 in Nightlife, Household, and Health Care Settings in Tokyo, Japan, in 2020

Key Points Question Which social settings are associated with large outbreaks and onward transmission of COVID-19? Findings In this case series study that analyzed 44 054 confirmed COVID-19 cases, transmission events in nightlife and health care settings were more likely to involve 5 or more cases. Household and health care cases were significantly less likely to generate onward transmission than nightlife cases. Meaning This case series highlights the heterogenic characteristics of social settings regarding their roles in COVID-19 transmission and the significance of nightlife settings for further COVID-19 spread.

eAppendix. Surveillance and Contact Tracing for COVID-19 in Tokyo and Areas Throughout Japan in 2020 The Infectious Diseases Act mandated reporting all suspected and confirmed COVID-19 cases in Japan starting January 6th, 2020. Public health officials interviewed everyone who tested positive for SARS-CoV-2 and identified contacts who would require quarantine and testing. This included conducting backward contact tracing to assess potential infectious sources within 14 days prior to symptom onset or confirmation, as well as forward contact tracing for 14 days. 1,2 Epidemiological data of each case were recorded in national databases; the National Epidemiological Surveillance of Infectious Disease, 3 and later in the Health Center Real-time Information-sharing System on  The first COVID-19 case was detected in Japan on January 16th, 2020. On January 28th, 2020, the Public Health Response in Tokyo and Areas throughout Japan in 2020 In Japan, there are no laws restricting the activities of individuals or companies with regard to public health measures. Although many countries implemented mobility restrictions in the early stages of the COVID-19 epidemic, the Japanese government requested its people to reduce human contact to control the COVID-19 spread, but these measures were optional and left to the discretion of the individual. 6 Tokyo is the capital of Japan, with an approximate population of 14 million as of October 1st, 2020, constituting 10% of Japan's total population. Furthermore, approximately 2.9 million people commute to Tokyo daily from neighboring prefectures for work or school. The first COVID-19 case in Japan was reported on January 16th in a prefecture next to Tokyo, and the first COVID-19 case in Tokyo was detected on January 23rd. The Tokyo Metropolitan Government (TMG) set up the Tokyo Metropolitan Emergency Management Council on Novel Coronavirus-Related Pneumonia on the same day. The TMG called for cooperation in COVID-19 control. The mobility restrictions employed by TMG -such as a request for remote work, stay-at-home, and canceling group events -also affected neighboring prefectures in the commuting area. These measures were issued as requests to citizens and companies in Tokyo, with no penalties for ignoring the restrictions.
The measures deployed by TMG are listed in chronological order (eText Table), which included a request for avoiding the "3 C's" ("Closed spaces with poor ventilation," "Crowded spaces with many people nearby," and "Close-contact settings such as close-range conversations"), business closures, limiting business hours, cancellation of mass gathering events, restricting event sizes and limiting seating capacity, encouraging remote work, and strengthening healthcare and PCR testing capacity.
The first COVID-19 superspreading event (SSE) detected in Tokyo was a New Year's party conducted on a party boat. In a press conference on March 30th, the Tokyo Governor requested citizens of Tokyo to refrain from visiting nightlife establishments. During the State of Emergency period, from April 11th to May 25th, restaurants and bars were requested to limit their business hours to between 5 am and 8 pm (excluding carryout and deliveries). After lifting the State of Emergency, the TMG continued requesting restaurants and bars to limit their business hours based on their roadmap of stepwise relaxation of infection control measures until June 18th. Early in the second surge in June, many SSEs were reported in Shinjuku and Ikebukuro, where large nightlife districts in Tokyo are located. The nightlife establishments with hosts and hostesses in those districts were connected to many reported SSEs. As a reaction, the Tokyo Governor publicly advised against visiting nightlife establishments (e.g., restaurants, bars, nightclubs with hosts and hostesses) in those areas. In the Shinjuku district, mass screening and more robust infection control measures were implemented, with active cooperation from owners and employees of nightlife establishments.
On July 22nd, the Japanese government began a nationwide campaign to promote domestic travel ("Go to Travel" campaign), excluding Tokyo. On October 1st, the Japanese government started a campaign to promote dining out ("Go to Eat" campaign) and expanded the "Go to Travel" campaign to include Tokyo. The TMG also commenced its own campaign to promote travel within Tokyo ("Motto Tokyo" campaign) later in October. Both the "Go to Eat" and "Motto Tokyo" campaigns, however, were canceled by the end of November due to the resurgence of COVID-19 cases (Wave 3), and the "Go to Travel" campaign was suspended in December. Throughout 2020, the TMG intermittently requested business closures or limiting-business-hour of restaurants and bars in April, May, June, August, September, November, and December.

Date
International and Japanese We defined a transmission setting as an occasion where the epidemiological link was identified, such as party, office, hospital, or household settings. One epidemiological link can involve multiple transmission settings; for example, if a party event results in transmission at an office and then at a household, cases in the same link were assigned to three different transmission settings: party, office, and household settings. A primary case was identified in each transmission setting: case A in a party, case B in an office, and cases C and D in respective households. The rest of the cases in transmission settings were defined as offspring cases. We did not identify primary cases in health care settings. Onward transmission is a transmission from one setting to another, shown in bold arrows. This study did not analyze multiple generations of transmission among offspring cases involved in the same transmission settings and onward transmission towards health care settings.
eTable 4. Number of Transmission Settings and Characteristics of their Primary Cases by the Number of Offspring Cases per Setting a Proportion of settings with offspring cases 1-4 / ≥ 5 were compared between nightlife setting and other settings using the χ2 test with Šidák corrections b The same primary case could be counted multiple times if he/she was a primary case of two or